Which of the method prevents metal from further corrosion?

One of the easiest and cheapest ways to prevent corrosion is to use barrier coatings like paint, plastic, or powder. 

Powders, including epoxy, nylon, and urethane, adhere to the metal surface to create a thin film. Plastic and waxes are often sprayed onto metal surfaces. 

Paint acts as a coating to protect the metal surface from the electrochemical charge that comes from corrosive compounds.